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+ <td><small>Copyright © 2001 - 2007 SILC Project<br />
+ <a href="http://silcnet.org">SILC Project Website</a></small></td>
+ <td align="right"><small>
+ <a href="index.html">SILC Toolkit Reference Manual</a><br />
+ <a href="toolkit_index.html">Index</a></small></td>
+ </small></td>
+ </tr>
+</table>
+<table border="0" cellspacing="0" cellpadding="0" width="100%">
+<tr bgcolor="#444444"><td><img src="space.gif" width="1" height="1"border="0" alt="" ></td></tr>
+</table>
+
+<table cellpadding="0" cellspacing="0" border="0">
+ <tr valign="top">
+
+ <td width="200" bgcolor="#f0f0f0">
+ <img src="space.gif" width="1" height="1" border="0" alt="">
+ <table width="100%" cellpadding="2" cellspacing="2" border="0">
+ <tr valign="top"><td>
+<br />
+<small>
+<!-- Template file for the big index that appears in the Toolkit reference
+manual on the left side. With this file it is possible to add other than
+automatically generated links to that list. -->
+
+<a href="index.html"><img src="box.gif" border="0" alt="">SILC Toolkit Reference Manual</a><br />
+
+
+<a href=silccryptlib.html><img src=box.gif border=0 alt=>SILC Crypto Library</a><br />
+ <a href=silcrng_intro.html><img src=box2.gif border=0 alt=>Introduction to SILC RNG</a><br />
+ <a href=silcrng.html><img src=box2.gif border=0 alt=>SILC RNG Interface</a><br />
+ <a href=silccipher.html><img src=box2.gif border=0 alt=>SILC Cipher API</a><br />
+ <a href=silcpkcs.html><img src=box2.gif border=0 alt=>SILC PKCS API</a><br />
+ <a href=silcpk.html><img src=box2.gif border=0 alt=>SILC Public Key API</a><br />
+ <a href=silcpkcs1.html><img src=box2.gif border=0 alt=>SILC PKCS #1 API</a><br />
+ <a href=silchash.html><img src=box2.gif border=0 alt=>SILC Hash Interface</a><br />
+ <a href=silchmac.html><img src=box2.gif border=0 alt=>SILC HMAC Interface</a><br />
+<a href=silccorelib.html><img src=box.gif border=0 alt=>SILC Core Library</a><br />
+ <a href=silcauth.html><img src=box2.gif border=0 alt=>SILC Authentication Interface</a><br />
+ <a href=silcmessage.html><img src=box2.gif border=0 alt=>SILC Message Interface</a><br />
+ <a href=silcchannel.html><img src=box2.gif border=0 alt=>SILC Channel Interface</a><br />
+ <a href=silccommand.html><img src=box2.gif border=0 alt=>SILC Command Interface</a><br />
+ <a href=silcnotify.html><img src=box2.gif border=0 alt=>SILC Notify Interface</a><br />
+ <a href=silcstatus.html><img src=box2.gif border=0 alt=>SILC Status Types</a><br />
+ <a href=silcmode.html><img src=box2.gif border=0 alt=>SILC Modes</a><br />
+ <a href=silcid.html><img src=box2.gif border=0 alt=>SILC ID Interface</a><br />
+ <a href=silcargument.html><img src=box2.gif border=0 alt=>SILC Argument Interface</a><br />
+ <a href=silcattrs.html><img src=box2.gif border=0 alt=>SILC Attributes Interface</a><br />
+ <a href=silcpacket.html><img src=box2.gif border=0 alt=>Packet Engine Interface</a><br />
+ <a href=silcpubkey.html><img src=box2.gif border=0 alt=>SILC Public Key Payload Interface</a><br />
+<a href=silcskelib.html><img src=box.gif border=0 alt=>SILC Key Exchange Library</a><br />
+ <a href=silcske.html><img src=box2.gif border=0 alt=>SILC SKE Interface</a><br />
+ <a href=silcconnauth.html><img src=box2.gif border=0 alt=>SILC Connection Authentication Interface</a><br />
+<a href=silcvcardlib.html><img src=box.gif border=0 alt=>SILC VCard Library</a><br />
+ <a href=silcvcard.html><img src=box2.gif border=0 alt=>SILC VCard Interface</a><br />
+<a href=silcmathlib.html><img src=box.gif border=0 alt=>SILC Math Library</a><br />
+ <a href=silcmp.html><img src=box2.gif border=0 alt=>SILC MP Interface</a><br />
+ <a href=silcmath.html><img src=box2.gif border=0 alt=>SILC Math Interface</a><br />
+<a href=silcclientlib.html><img src=box.gif border=0 alt=>SILC Client Library</a><br />
+ <a href=silcclient_using.html><img src=box2.gif border=0 alt=>Using SILC Client Library Tutorial</a><br />
+ <a href=command_reply_args.html><img src=box2.gif border=0 alt=>Arguments for <b>command_reply</b> Client Operation</a><br />
+ <a href=silcstatus_args.html><img src=box2.gif border=0 alt=>SilcStatus Error Arguments in <b>command_reply</b> Client Operation</a><br />
+ <a href=notifyargs.html><img src=box2.gif border=0 alt=>Arguments for <b>notify</b> Client Operation</a><br />
+ <a href=silcclient_unicode.html><img src=box2.gif border=0 alt=>Unicode and UTF-8 Strings in Client Library</a><br />
+ <a href=silcclient.html><img src=box2.gif border=0 alt=>Client Library Interface Reference</a><br />
+ <a href=silcclient_entry.html><img src=box2.gif border=0 alt=>Client Entry Interface Reference</a><br />
+<a href=silcasn1lib.html><img src=box.gif border=0 alt=>SILC ASN.1 Library</a><br />
+ <a href=silcasn1.html><img src=box2.gif border=0 alt=>SILC ASN.1 Interface</a><br />
+ <a href=silcber.html><img src=box2.gif border=0 alt=>SILC BER interface</a><br />
+<a href=silchttplib.html><img src=box.gif border=0 alt=>SILC HTTP Library</a><br />
+ <a href=silchttpserver.html><img src=box2.gif border=0 alt=>SILC HTTP Server Interface</a><br />
+ <a href=silchttpphp.html><img src=box2.gif border=0 alt=>SILC HTTP PHP Translator</a><br />
+<a href=silcutillib.html><img src=box.gif border=0 alt=>SILC Utility Library</a><br />
+ <a href=silctypes.html><img src=box2.gif border=0 alt=>Basic Types and Definitions</a><br />
+ <a href=silcbuffer.html><img src=box2.gif border=0 alt=>Data Buffer Interface</a><br />
+ <a href=silcbuffmt.html><img src=box2.gif border=0 alt=>Data Buffer Format Interface</a><br />
+ <a href=silchashtable.html><img src=box2.gif border=0 alt=>Hash Table Interface</a><br />
+ <a href=silcmemory.html><img src=box2.gif border=0 alt=>Memory Allocation Interface</a><br />
+ <a href=silcstack.html><img src=box2.gif border=0 alt=>Data Stack (memory pool) Interface</a><br />
+ <a href=silcfsm.html><img src=box2.gif border=0 alt=>Finite State Machine Interface</a><br />
+ <a href=silcthread.html><img src=box2.gif border=0 alt=>Thread Interface</a><br />
+ <a href=silcmutex.html><img src=box2.gif border=0 alt=>Mutual Exclusion Lock Interface</a><br />
+ <a href=silccond.html><img src=box2.gif border=0 alt=>Condition Variable Interface</a><br />
+ <a href=silcatomic.html><img src=box2.gif border=0 alt=>Atomic Operations Interface</a><br />
+ <a href=silcnet.html><img src=box2.gif border=0 alt=>Network (TCP and UDP) Interface</a><br />
+ <a href=silcschedule.html><img src=box2.gif border=0 alt=>Scheduler Interface</a><br />
+ <a href=silcasync.html><img src=box2.gif border=0 alt=>Asynchronous Operation Interface</a><br />
+ <a href=silcstream.html><img src=box2.gif border=0 alt=>Abstract Stream Interface</a><br />
+ <a href=silcsocketstream.html><img src=box2.gif border=0 alt=>Socket Stream Interface</a><br />
+ <a href=silcfdstream.html><img src=box2.gif border=0 alt=>File Descriptor Stream Interface</a><br />
+ <a href=silcfileutil.html><img src=box2.gif border=0 alt=>File Utility Functions</a><br />
+ <a href=silcstrutil.html><img src=box2.gif border=0 alt=>String Utility Interface</a><br />
+ <a href=silcsnprintf.html><img src=box2.gif border=0 alt=>Snprintf Interface</a><br />
+ <a href=silcutf8.html><img src=box2.gif border=0 alt=>UTF-8 String Interface</a><br />
+ <a href=silcstringprep.html><img src=box2.gif border=0 alt=>Stringprep Interface</a><br />
+ <a href=silcutil.html><img src=box2.gif border=0 alt=>Utility Functions</a><br />
+ <a href=silclist.html><img src=box2.gif border=0 alt=>List Interface</a><br />
+ <a href=silcdlist.html><img src=box2.gif border=0 alt=>Dynamic List Interface</a><br />
+ <a href=silcmime.html><img src=box2.gif border=0 alt=>MIME Interface</a><br />
+ <a href=silctime.html><img src=box2.gif border=0 alt=>Time Utility Functions</a><br />
+ <a href=silclog.html><img src=box2.gif border=0 alt=>Logging Interface</a><br />
+ <a href=silcconfig.html><img src=box2.gif border=0 alt=>Config File Interface</a><br />
+<a href=silcskrlib.html><img src=box.gif border=0 alt=>SILC Key Repository Library</a><br />
+ <a href=silcskr.html><img src=box2.gif border=0 alt=>SILC SKR Interface</a><br />
+<a href=silcaputillib.html><img src=box.gif border=0 alt=>SILC Application Utility Library</a><br />
+ <a href=silcapputil.html><img src=box2.gif border=0 alt=>SILC Application Utilities</a><br />
+ <a href=silcidcache.html><img src=box2.gif border=0 alt=>SILC ID Cache Interface</a><br />
+<a href=silcsftplib.html><img src=box.gif border=0 alt=>SILC SFTP Library</a><br />
+ <a href=silcsftp.html><img src=box2.gif border=0 alt=>SILC SFTP Interface</a><br />
+ <a href=silcsftp_fs.html><img src=box2.gif border=0 alt=>SFTP Filesystems Interface</a><br />
+
+<br />
+<b>Resource Links</b>
+<br />
+<a href="http://silcnet.org"><img src="box.gif" border="0" alt="">SILC Project Website</a><br />
+<a href="http://silcnet.org/support/documentation/"><img src="box.gif" border="0" alt="">SILC Protocol Documentation</a><br />
+<a href="http://silcnet.org/support/documentation/wp/"><img src="box.gif" border="0" alt="">SILC White Paper</a><br />
+<a href="http://silcnet.org/support/faq/"><img src="box.gif" border="0" alt="">SILC FAQs</a><br />
+
+</small>
+<br /><br /><br /><br />
+ </td></tr>
+ </table>
+ </td>
+
+ <td bgcolor="#cccccc" background="dot.gif">
+ <img src="space.gif" width="1" height="1" border="0" alt=""></td>
+
+ <td width="720" bgcolor="#ffffff">
+ <img src="space.gif" width="1" height="1" border="0" alt="">
+ <table cellpadding="2" cellspacing="6" width="100%">
+ <tr><td valign="top">
+<br />
+<big><b>Introduction to Random Number Generator</b></big>
+
+<br /> <br /> <br />
+<b>Overview</b>
+
+<br /> <br />
+SILC Random Number Generator is cryptographically strong pseudo random
+number generator. It is used to generate all the random numbers needed
+in the SILC sessions. All key material and other sources needing random
+numbers use this generator.
+
+<br /> <br />
+The RNG has a random pool of 1024 bytes of size that provides the actual
+random numbers for the application. The pool is initialized when the
+RNG is allocated and initialized with silc_rng_alloc and silc_rng_init
+functions, respectively.
+
+
+<br /> <br /> <br />
+<b>Random Pool Initialization</b>
+
+<br /> <br />
+The RNG's random pool is the source of all random output data. The pool is
+initialized with silc_rng_init and application can reseed it at any time
+by calling the silc_rng_add_noise function.
+
+<br /> <br />
+The initializing phase attempts to set the random pool in a state that it
+is impossible to learn the input data to the RNG or any random output
+data. This is achieved by acquiring noise from various system sources. The
+first source is called to provide "soft noise". This noise is various
+data from system's processes. The second source is called to provide
+"medium noise". This noise is various output data from executed commands.
+Usually the commands are Unix `ps' and `ls' commands with various options.
+The last source is called to provide "hard noise" and is noise from
+system's /dev/random, if it exists.
+
+
+<br /> <br /> <br />
+<b>Stirring the Random Pool</b>
+
+<br /> <br />
+Every time data is acquired from any source, the pool is stirred. The
+stirring process performs an CFB (cipher feedback) encryption with SHA1
+algorithm to the entire random pool. First it acquires an IV (Initial
+Vector) from the constant (random) location of the pool and performs
+the first CFB pass. Then it acquires a new encryption key from variable
+location of the pool and performs the second CFB pass. The encryption
+key thus is always acquired from unguessable data.
+
+<br /> <br />
+The encryption process to the entire random pool assures that it is
+impossible to learn the input data to the random pool without breaking the
+encryption process. This would effectively mean breaking the SHA1 hash
+function. The encryption process also assures that each random output from
+the random pool is secured with cryptographically strong function, the
+SHA1 in this case.
+
+<br /> <br />
+The random pool can be restirred by the application at any point by
+calling the silc_rng_add_noise function. This function adds new noise to
+the pool and then stirs the entire pool.
+
+
+<br /> <br /> <br />
+<b>Stirring Thresholds</b>
+
+<br /> <br />
+The random pool has two thresholds that controls when the random pool
+needs more new noise and requires restirring. As previously mentioned, the
+application may do this by calling the silc_rng_add_noise. However, the
+RNG performs this also automatically.
+
+<br /> <br />
+The first threshold gets soft noise from system and stirs the random pool.
+The threshold is reached after 64 bits of random data has been fetched
+from the RNG. After the 64 bits, the soft noise acquiring and restirring
+process is performed every 8 bits of random output data until the second
+threshold is reached.
+
+<br /> <br />
+The second threshold gets hard noise from system and stirs the random
+pool. The threshold is reached after 160 bits of random output. After the
+noise is acquired (from /dev/urandom) the random pool is stirred and the
+thresholds are set to zero. The process is repeated again after 64 bits of
+output for first threshold and after 160 bits of output for the second
+threshold.
+
+
+<br /> <br /> <br />
+<b>Internal State of the Random Pool</b>
+
+<br /> <br />
+The random pool has also internal state that provides several variable
+distinct points to the random pool where the data is fetched. The state
+changes every 8 bits of output data and it is guaranteed that the fetched
+8 bits of data is from distinct location compared to the previous 8 bits.
+It is also guaranteed that the internal state never wraps before
+restirring the entire random pool. The internal state means that the data
+is not fetched linearly from the pool, eg. starting from zero and wrapping
+at the end of the pool. The internal state is not dependent of any random
+data in the pool. The internal states are initialized (by default the pool
+is splitted to four different sections (states)) at the RNG
+initialization phase. The state's current position is added linearly and
+wraps at the the start of the next state. The states provides the distinct
+locations.
+
+
+<br /> <br /> <br />
+<b>Security Considerations</b>
+
+<br /> <br />
+The security of this random number generator, like of any other RNG's,
+depends of the initial state of the RNG. The initial state of the random
+number generators must be unknown to an adversary. This means that after
+the RNG is initialized it is required that the input data to the RNG and
+the output data to the application has no correlation of any kind that
+could be used to compromise the acquired random numbers or any future
+random numbers.
+
+<br /> <br />
+It is, however, clear that the correlation exists but it needs to be
+hard to solve for an adversary. To accomplish this the input data to the
+random number generator needs to be secret. Usually this is impossible to
+achieve. That is why SILC's RNG acquires the noise from three different
+sources and provides for the application an interface to add more noise at
+any time. The first source ("soft noise") is known to the adversary but
+requires exact timing to get all of the input data. However, getting only
+partial data is easy. The second source ("medium noise") depends on the
+place of execution of the application. Getting at least partial data is
+easy but securing for example the user's home directory from outside access
+makes it harder. The last source ("hard noise") is considered to be the
+most secure source of data. An adversary is not considered to have any
+access on this data. This of course greatly depends on the operating system.
+
+<br /> <br />
+These three sources are considered to be adequate since the random pool is
+relatively large and the output of each bit of the random pool is secured
+by cryptographically secure function, the SHA1 in CFB mode encryption.
+Furthermore the application may provide other random data, such as random
+key strokes or mouse movement to the RNG. However, it is recommended that
+the application would not be the single point of source for the RNG, in
+either intializing or reseeding phases later in the session. Good solution
+is probably to use both, the application's seeds and the RNG's own
+sources, equally.
+
+<br /> <br />
+The RNG must also assure that any old or future random numbers are not
+compromised if an adversary would learn the initial input data (or any
+input data for that matter). The SILC's RNG provides good protection for
+this even if the some of the input bits would be compromised for old or
+future random numbers. The RNG reinitalizes (reseeds) itself using the
+thresholds after every 64 and 160 bits of output. This is considered to be
+adequate even if some of the bits would get compromised. Also, the
+applications that use the RNG usually fetches at least 256 bits from the
+RNG. This means that everytime RNG is accessed both of the thresholds are
+reached. This should mean that the RNG is never too long in an compromised
+state and recovers as fast as possible.
+
+
+<br /> <br /> <br />
+<b>Caveat Windows Programmer</b>
+
+<br /> <br />
+The caller must be cautios when using this RNG with native WIN32 system.
+The RNG most likely is impossible to set in unguessable state just by
+using the RNG's input data sources. On WIN32 it is stronly suggested
+that caller would add more random noise after the initialization of the
+RNG using the silc_rng_add_noise function. For example, random mouse
+movements may be used.
+
+<br /><br /><br /><br />
+ </td></tr>
+ </table>
+ </td>
+
+ <td bgcolor="#cccccc" background="dot.gif">
+ <img src="space.gif" width="1" height="1" border="0" alt=""></td>
+
+ <td width="180" bgcolor="#f0f0f0">
+ <img src="space.gif" width="1" height="1" border="0" alt="">
+ <table width="100%" cellpadding="4" cellspacing="0">
+ <tr valign="top"><td>
+<br />
+<font face="Helvetica,Arial,Sans-serif" size="1">
+</font>
+
+<br /><br /><br /><br />
+ </td></tr>
+ </table>
+ </td>
+</tr>
+</table>
+
+<table border="0" cellspacing="0" cellpadding="0" width="100%">
+<tr bgcolor="#444444"><td><img src="space.gif" width="1" height="1"border="0" alt="" ></td></tr>
+</table>
+<table border="0" cellspacing="0" cellpadding="6" width="100%">
+ <tr valign="top" bgcolor="#dddddd">
+ <td><small>Copyright © 2001 - 2007 SILC Project<br />
+ <a href="http://silcnet.org">SILC Project Website</a></small></td>
+ <td align="right"><small>
+ <a href="index.html">SILC Toolkit Reference Manual</a><br />
+ <a href="toolkit_index.html">Index</a></small></td>
+ </small></td>
+ </tr>
+</table>
+
+</body>
+</html>
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